Model Stacey McKenzie’s famously unconventional looks are proving a challenge for the producers of “Ugly,” a biopic on her.

We’re told that after a traditional casting search turned up nobody suitable for the part, Ken Mok — who produced “Joy” — is holding a “Willy Wonka-style” open casting for the parts of McKenzie at age 10 and as a teen.

Mok told Page Six that anyone 5-foot-7 or taller would be considered. “So far we haven’t found the right person,” he said. “We’re starting to get nervous.”